14 July 2009

the process of replacing old side-wall boards in large dug-out spaces (e.g., Pit 91).

This post will serve as both an introduction to some of the "other work" that excavators (and excavatrices) perform at Rancho La Brea and a documentation of the particular method of shoring board replacement that the Lone Male Excavator has developed.

So as the thick boards holding up the side walls of Pit 91 grow old, they often bow out, rot out, or both. Up above the pit, 14ft x 11 3/4" x 2 3/4" boards are stored ready to be cut to an average of about 75" long for use as a shoring board.

After a board is slated for replacement, of course it must be extracted. This is commonly far more difficult than it sounds. If the board is rotted to extremes on the ends locked in by the I-beams, then it is not too tough for a hatchet to cut through one end and pry the board out with a crowbar. If the board is not rotted away much at the ends, however, (as the boards pictured here) it can be quite difficult.

Initially, a cut with a circular saw is made through the board(s) being replaced. This is very dangerous and every safety precaution must be taken at this point (e.g., clean goggles, steady hands, hard hat). It is also messy and anything, including one self, which should not get covered in sawdust should be protected. If two parallel cuts, about 2" apart are made, extraction will be easier. Our cordless circular saw, however, does not cut deep enough to go through to the back of the boards. So I have added to this method inspired by the wisdom of William A. Akersten's thought on sabertooth cat incisor (front teeth) functional morphology.

The points on large, cone-shaped incisors of Smilodon fatalis are separated to the extent that when they pinch together top to bottom and pierce into the skin of prey, they are thought to create a perforated line which allows for easy tearing off of chunks of flesh. When we are unable to pry/break out a board along the saw cuts, holes can be drilled along the cuts to create such perforated lines which can then be hacked trough easily or broken out through prying.Once a board is out, the wall of earth, often asphalt saturated, must be shaved a little with hand tools or, in dire need, a pneumatic chipper. Occasionally fossils are found in the side walls, so these must be watched for and documented when discovered.

Depending on the thickness of the new board and the bowing out of the old board shaving the walls may take up to a couple hours. Once this is done a measurement for the new board's length is taken, giving about an inch and a half behind the lip of each I-beam. (Often, when you think you've shaved enough and try to get the new board in, you find that a few spots need more shaving. The first of these two pictured here took me 3 attempts. I also found that I had cut it too long and had to take an inch off one end.)

After you've seen that the board will fit the space you've shaved out of the earth-wall, you must get it equally situated behind the lip of each I-beam... not so hard when you've got two-three boards out and you are doing the bottom board, but if you are trying to slide a single board over in a single space (like w/ the second board pictured) it can sometimes involve a long trial messing with crowbars. I have no solution, except putting in the lag screws early and trying to use them to slide the board. This does not often work.

If gaps are left, they are reduced by placing thin pieces of wood at the bottom of boards.

The boards are locked in between (and behind the lip of) I-beams which run about 40 ft under ground. As much of the board as possible is slid behind the inside of the I-beam before 5/16" holes are drilled beside the lip of the I-beam for 9/16" x 3 3/4" lag screws. The lag screws go through, what I'm gonna call, giant square washers which tighten the board flush to the I-beam. A thin, small piece of plywood is often needed between the shoring board and the giant square washer.There you have it; Shoring 101. The final exam is getting a board replaced and not injuring yourself in the process.

So the Lone Male Excavator is off to grad school. This is my last day as an excavator at the Page Museum at Rancho La Brea, but I will still be around in spirit. (In fact don't be too surprised to see posts in the future by The Ghost of the Lone Male Excavator.)

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